>     STDIN->blocking(0);

That part is the problem. Net::Server tries to handle SSL in a special way but this way is not working with the code you use. The blocking(0) will not be done on the socket to the client, but instead on fd 0 which is at this moment /dev/null. Thus it will not have the desired effect.

One way to deal with the problem is to reach into the internals of Net::Server to get access to the real file descriptor behind STDIN:

tied(*STDIN)->[0]->blocking(0);

A better way is to use the file descriptor which is given to the process_request function:

sub process_request {
    my ($self,$fd) = @_;
    $fd->blocking(0);

In both variants the real socket will be set non-blocking.

Apart from that, note that the SSL handshake will still be done blocking by Net::Server.